Chapter 1 Introduction. © 2004 Pearson Addison-Wesley. All rights reserved1-2 Focus of the Course Object-Oriented Software Development problem solving.

Chapter 1

Introduction

© 2004 Pearson Addison-Wesley. All rights reserved 1-2

Focus of the Course

• Object-Oriented Software Development

problem solving

program design, implementation, and testing

object-oriented concepts• classes

• objects

• encapsulation

• inheritance

• polymorphism

graphical user interfaces

the Java programming language


Introduction

• We first need to explore the fundamentals of computer processing

• Chapter 1 focuses on:

components of a computer how those components interact how computers store and manipulate information computer networks the Internet and the World Wide Web programming and programming languages an introduction to Java an overview of object-oriented concepts


Outline

Computer Processing

Hardware Components

Networks

The Java Programming Language

Program Development

Object-Oriented Programming


Hardware and Software

• Hardware the physical, tangible parts of a computer keyboard, monitor, disks, wires, chips, etc.

• Software programs and data a program is a series of instructions

• A computer requires both hardware and software

• Each is essentially useless without the other


CPU and Main Memory

CentralProcessing

Unit

MainMemory

Chip that executes program commands

Intel Pentium 4Sun ultraSPARC IIIPrimary storage

area for programs and

data that are in active use

Synonymous with RAM


Secondary Memory Devices

CentralProcessing

Unit

MainMemory

Floppy Disk

Hard Disk

Secondary memorydevices providelong-term storage

Information is movedbetween main memoryand secondary memoryas needed

Hard disksFloppy disksZIP disksWritable CDsWritable DVDsTapes


Input / Output Devices

CentralProcessing

Unit

MainMemory

Floppy Disk

Hard Disk

Monitor

Keyboard

I/O devices facilitateuser interaction

Monitor screenKeyboardMouseJoystickBar code scannerTouch screen


Software Categories

• Operating System controls all machine activities provides the user interface to the computer manages resources such as the CPU and memory Windows XP, Unix, Linux, Mac OS

• Application program generic term for any other kind of software word processors, missile control systems, games

• Most operating systems and application programs have a graphical user interface (GUI)


Analog vs. Digital

• There are two basic ways to store and manage data:

• Analog continuous, in direct proportion to the data represented music on a record album - a needle rides on ridges in the

grooves that are directly proportional to the voltages sent to the speaker

• Digital the information is broken down into pieces, and each

piece is represented separately music on a compact disc - the disc stores numbers

representing specific voltage levels sampled at specific times


Digital Information

• Computers store all information digitally: numbers text graphics and images video audio program instructions

• In some way, all information is digitized - broken down into pieces and represented as numbers


Representing Text Digitally

• For example, every character is stored as a number, including spaces, digits, and punctuation

• Corresponding upper and lower case letters are separate characters

H i , H e a t h e r .

72 105 44 32 72 101 97 116 104 101 114 46


Binary Numbers

• Once information is digitized, it is represented and stored in memory using the binary number system

• A single binary digit (0 or 1) is called a bit

• Devices that store and move information are cheaper and more reliable if they have to represent only two states

• A single bit can represent two possible states, like a light bulb that is either on (1) or off (0)

• Permutations of bits are used to store values


Bit Permutations

1 bit

01

2 bits

00011011

3 bits

000001010011100101110111

4 bits

00000001001000110100010101100111

10001001101010111100110111101111

Each additional bit doubles the number of possible permutations


Bit Permutations

• Each permutation can represent a particular item

• There are 2N permutations of N bits

• Therefore, N bits are needed to represent 2N unique items

21 = 2 items

22 = 4 items

23 = 8 items

24 = 16 items

25 = 32 items

1 bit ?

2 bits ?

3 bits ?

4 bits ?

5 bits ?

How manyitems can be

represented by


Outline

Computer Processing

Hardware Components

Networks


Program Development



A Computer Specification

• Consider the following specification for a personal computer:

2.8 GHz Pentium 4 Processor 512 MB RAM 80 GB Hard Disk 48x CD-RW / DVD-ROM Combo Drive 17” Video Display with 1280 x 1024 resolution 56 Kb/s Modem

• What does it all mean?


Memory

Main memory is divided into many memory locations (or cells)

927892799280928192829283928492859286

Each memory cell has a numeric address, which uniquely identifies it


Storing Information

927892799280928192829283928492859286

Large values arestored in consecutivememory locations

1001101010011010Each memory cell stores a set number of bits (usually 8 bits, or one byte)


Storage Capacity

• Every memory device has a storage capacity, indicating the number of bytes it can hold

• Capacities are expressed in various units:

KB 210 = 1024

MB 220 (over 1 million)

GB 230 (over 1 billion)

TB 240 (over 1 trillion)

Unit Symbol Number of Bytes

kilobyte

megabyte

gigabyte

terabyte


Memory

• Main memory is volatile - stored information is lost if the electric power is removed

• Secondary memory devices are nonvolatile

• Main memory and disks are direct access devices - information can be reached directly

• The terms direct access and random access often are used interchangeably

• A magnetic tape is a sequential access device since its data is arranged in a linear order - you must get by the intervening data in order to access other information


RAM vs. ROM

• RAM - Random Access Memory (direct access)

• ROM - Read-Only Memory

• The terms RAM and main memory are basically interchangeable

• ROM could be a set of memory chips, or a separate device, such as a CD ROM

• Both RAM and ROM are random (direct) access devices!

• RAM probably should be called Read-Write Memory


Compact Discs

• A CD-ROM is portable read-only memory

• A microscopic pit on a CD represents a binary 1 and a smooth area represents a binary 0

• A low-intensity laser reflects strongly from a smooth area and weakly from a pit

• A CD-Recordable (CD-R) drive can be used to write information to a CD once

• A CD-Rewritable (CD-RW) can be erased and reused

• The speed of a CD drive indicates how fast (max) it can read and write information to a CD


DVDs

• A DVD is the same size as a CD, but can store much more information

• The format of a DVD stores more bits per square inch

• A CD can store 650 MB, while a standard DVD can store 4.7 GB A double sided DVD can store 9.4 GB

Other advanced techniques can bring the capacity up to 17.0 GB

• Like CDs, there are DVD-R and DVD-RW discs


The Central Processing Unit

• A CPU is on a chip called a microprocessor

• It continuously follows the fetch-decode-execute cycle:

fetch

Retrieve an instruction from main memory

decode

Determine what theinstruction is

execute

Carry out theinstruction



• The CPU contains:

Arithmetic / Logic Unit

Registers

Control Unit

Small storage areas

Performs calculations and makes decisions

Coordinates processing steps



• The speed of a CPU is controlled by the system clock

• The system clock generates an electronic pulse at regular intervals

• The pulses coordinate the activities of the CPU

• The speed is usually measured in gigahertz (GHz)


Monitor

• The size of a monitor (17") is measured diagonally, like a television screen

• Most monitors these days have multimedia capabilities: text, graphics, video, etc.

• A monitor has a certain maximum resolution , indicating the number of picture elements, called pixels, that it can display (such as 1280 by 1024)

• High resolution (more pixels) produces sharper pictures


Modem

• Data transfer devices allow information to be sent and received between computers

• Many computers include a modulator-demodulator or modem, which allows information to be moved across a telephone line

• A data transfer device has a maximum data transfer rate

• A modem, for instance, may have a data transfer rate of 56,000 bits per second (bps)


Outline

Computer Processing

Hardware Components

Networks


Program Development



Networks

• A network is two or more computers that are connected so that data and resources can be shared

• Most computers are connected to some kind of network

• Each computer has its own network address, which uniquely identifies it among the others

• A file server is a network computer dedicated to storing programs and data that are shared among network users


Network Connections

• Each computer in a network could be directly connected to every other computer in the network

• These are called point-to-point connections

This technique is not practical formore than a few close machines

Adding a computer requiresa new communication linefor each computer alreadyin the network


Network Connections

• Most networks share a single communication line

• Adding a new computer to the network is relatively easy

Network traffic must taketurns using the line, whichintroduces delays

Often information is brokendown in parts, called packets,which are sent to the receivingmachine and then reassembled


Local-Area Networks

LAN

A Local-Area Network(LAN) covers a smalldistance and a smallnumber of computers

A LAN often connects the machinesin a single room or building


Wide-Area Networks

LAN

A Wide-Area Network (WAN)connects two or more LANs,often over long distances

A LAN usually is ownedby one organization, buta WAN often connectsgroups in different countries

LAN


The Internet

• The Internet is a WAN which spans the entire planet

• The word Internet comes from the term internetworking

• It started as a United States government project, sponsored by the Advanced Research Projects Agency (ARPA) - originally it was called the ARPANET

• The Internet grew quickly throughout the 1980s and 90s


TCP/IP

• A protocol is a set of rules that determine how things communicate with each other

• The software which manages Internet communication follows a suite of protocols called TCP/IP

• The Internet Protocol (IP) determines the format of the information as it is transferred

• The Transmission Control Protocol (TCP) dictates how messages are reassembled and handles lost information


IP and Internet Addresses

• Each computer on the Internet has a unique IP address, such as:

204.192.116.2

• Most computers also have a unique Internet name, which also is referred to as an Internet address:

spencer.villanova.edu

kant.gestalt-llc.com

• The first part indicates a particular computer (spencer)

• The rest is the domain name, indicating the organization (villanova.edu)


Domain Names

• The last part of a domain name, called a top-level domain (TLD), indicates the type of organization:

educomorgnet

- educational institution- commercial entity- non-profit organization- network-based organization

Sometimes the suffixindicates the country: New TLDs have

recently been added:

biz, info, tv, name

ukaucase

- United Kingdom- Australia- Canada- Sweden


Domain Names

• A domain name can have several parts

• Unique domain names mean that multiple sites can have individual computers with the same local name

• When used, an Internet address is translated to an IP address by software called the Domain Name System (DNS)

• There is no one-to-one correspondence between the sections of an IP address and the sections of an Internet address


The World Wide Web

• The World Wide Web allows many different types of information to be accessed using a common interface

• A browser is a program which accesses and presents information

text, graphics, video, sound, audio, executable programs

• A Web document usually contains links to other Web documents, creating a hypermedia environment

• The term Web comes from the fact that information is not organized in a linear fashion


The World Wide Web

• Web documents are often defined using the HyperText Markup Language (HTML)

• Information on the Web is found using a Uniform Resource Locator (URL):

http://www.lycos.com

http://www.villanova.edu/webinfo/domains.html

ftp://java.sun.com/applets/animation.zip

• A URL indicates a protocol (http), a domain, and possibly specific documents


Outline

Computer Processing

Hardware Components

Networks


Program Development



Java

• A programming language specifies the words and symbols that we can use to write a program

• A programming language employs a set of rules that dictate how the words and symbols can be put together to form valid program statements

• The Java programming language was created by Sun Microsystems, Inc.

• It was introduced in 1995 and it's popularity has grown quickly since


Java Program Structure

• In the Java programming language: A program is made up of one or more classes A class contains one or more methods A method contains program statements

• These terms will be explored in detail throughout the course

• A Java application always contains a method called main

• See Lincoln.java (page 28)



public class MyProgram

{

}

// comments about the class

class header

class body

Comments can be placed almost anywhere



public class MyProgram

{

}

// comments about the class

public static void main (String[] args)

{

}

// comments about the method

method headermethod body


Comments• Comments in a program are called inline

documentation

• They should be included to explain the purpose of the program and describe processing steps

• They do not affect how a program works

• Java comments can take three forms:

// this comment runs to the end of the line

/* this comment runs to the terminating symbol, even across line breaks */

/** this is a javadoc comment */


Identifiers

• Identifiers are the words a programmer uses in a program

• An identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign

• Identifiers cannot begin with a digit

• Java is case sensitive - Total, total, and TOTAL are different identifiers

• By convention, programmers use different case styles for different types of identifiers, such as title case for class names - Lincoln

upper case for constants - MAXIMUM


Identifiers

• Sometimes we choose identifiers ourselves when writing a program (such as Lincoln)

• Sometimes we are using another programmer's code, so we use the identifiers that he or she chose (such as println)

• Often we use special identifiers called reserved words that already have a predefined meaning in the language

• A reserved word cannot be used in any other way


Reserved Words

• The Java reserved words:

abstractbooleanbreakbytecasecatchcharclassconstcontinuedefaultdodouble

elseenumextendsfalsefinalfinallyfloatforgotoifimplementsimportinstanceof

intinterfacelongnativenewnullpackageprivateprotectedpublicreturnshortstatic

strictfpsuperswitchsynchronizedthisthrowthrowstransienttruetryvoidvolatilewhile


White Space

• Spaces, blank lines, and tabs are called white space

• White space is used to separate words and symbols in a program

• Extra white space is ignored

• A valid Java program can be formatted many ways

• Programs should be formatted to enhance readability, using consistent indentation

• See Lincoln2.java (page 34)

• See Lincoln3.java (page 35)


Outline

Computer Processing

Hardware Components

Networks


Program Development



Program Development

• The mechanics of developing a program include several activities

writing the program in a specific programming language (such as Java)

translating the program into a form that the computer can execute

investigating and fixing various types of errors that can occur

• Software tools can be used to help with all parts of this process


Language Levels

• There are four programming language levels: machine language assembly language high-level language fourth-generation language

• Each type of CPU has its own specific machine language

• The other levels were created to make it easier for a human being to read and write programs


Programming Languages

• Each type of CPU executes only a particular machine language

• A program must be translated into machine language before it can be executed

• A compiler is a software tool which translates source code into a specific target language

• Often, that target language is the machine language for a particular CPU type

• The Java approach is somewhat different


Java Translation

• The Java compiler translates Java source code into a special representation called bytecode

• Java bytecode is not the machine language for any traditional CPU

• Another software tool, called an interpreter, translates bytecode into machine language and executes it

• Therefore the Java compiler is not tied to any particular machine

• Java is considered to be architecture-neutral


Java Translation

Java sourcecode

Machinecode

Javabytecode

Bytecodeinterpreter

Bytecodecompiler

Javacompiler


Development Environments

• There are many programs that support the development of Java software, including:

Sun Java Development Kit (JDK) Sun NetBeans IBM Eclipse Borland JBuilder MetroWerks CodeWarrior Monash BlueJ

• Though the details of these environments differ, the basic compilation and execution process is essentially the same


Syntax and Semantics

• The syntax rules of a language define how we can put together symbols, reserved words, and identifiers to make a valid program

• The semantics of a program statement define what that statement means (its purpose or role in a program)

• A program that is syntactically correct is not necessarily logically (semantically) correct

• A program will always do what we tell it to do, not what we meant to tell it to do


Errors

• A program can have three types of errors

• The compiler will find syntax errors and other basic problems (compile-time errors)

If compile-time errors exist, an executable version of the program is not created

• A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)

• A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)


Basic Program Development

errors

errors

Edit andsave program

Compile program

Execute program andevaluate results


Outline

Computer Processing

Hardware Components

Networks


Program Development



Problem Solving

• The purpose of writing a program is to solve a problem

• Solving a problem consists of multiple activities:

Understand the problem

Design a solution

Consider alternatives and refine the solution

Implement the solution

Test the solution

• These activities are not purely linear – they overlap and interact


Problem Solving

• The key to designing a solution is breaking it down into manageable pieces

• When writing software, we design separate pieces that are responsible for certain parts of the solution

• An object-oriented approach lends itself to this kind of solution decomposition

• We will dissect our solutions into pieces called objects and classes



• Java is an object-oriented programming language

• As the term implies, an object is a fundamental entity in a Java program

• Objects can be used effectively to represent real-world entities

• For instance, an object might represent a particular employee in a company

• Each employee object handles the processing and data management related to that employee


Objects

• An object has:

state - descriptive characteristics

behaviors - what it can do (or what can be done to it)

• The state of a bank account includes its current balance

• The behaviors associated with a bank account include the ability to make deposits and withdrawals

• Note that the behavior of an object might change its state


Classes

• An object is defined by a class

• A class is the blueprint of an object

• The class uses methods to define the behaviors of the object

• The class that contains the main method of a Java program represents the entire program

• A class represents a concept, and an object represents the embodiment of that concept

• Multiple objects can be created from the same class


Objects and Classes

Bank Account

A class(the concept)

John’s Bank AccountBalance: $5,257

An object(the realization)

Bill’s Bank AccountBalance: $1,245,069

Mary’s Bank AccountBalance: $16,833

Multiple objectsfrom the same class


Inheritance• One class can be used to derive another via

inheritance

• Classes can be organized into hierarchies

Bank Account

Account

Charge Account

Savings Account

Checking Account


Summary

• Chapter 1 focused on:

components of a computer how those components interact how computers store and manipulate information computer networks the Internet and the World Wide Web programming and programming languages an introduction to Java an overview of object-oriented concepts

Chapter 1 Introduction. © 2004 Pearson Addison-Wesley. All rights reserved1-2 Focus of the Course Object-Oriented Software Development problem solving.

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